Not applicable.
Not applicable.
This invention is in the field of anti-icing systems for roads and bridges, and is more specifically directed to roadway covering systems.
The icing and snow-covering of roadways is of course a well-known cause of poor vehicle traction, and thus poor driving conditions, during the winter season in many parts of the world. These poor driving conditions result in motor vehicle collisions, and also in reduced traffic flow as vehicles slow in attempting to prevent collisions.
Bridges are especially susceptible to dangerous icing, especially in souther parts of the United States, which often have temperatures around freezing, and also often receive freezing rain and sleet in winter months. An example of a particularly dangerous icing condition is referred to as xe2x80x9cblack icexe2x80x9d. Because bridge span portions are not in direct contact with the earth, which retains heat from earlier in the day, bridges generally ice sooner than the rest of the roadways in these conditions. Accordingly, cities, states, and other road maintenance entities continue to take significant anti-icing and de-icing actions in winter to maintain or improve roadway and bridge traction. By way of definition, the term xe2x80x9canti-icingxe2x80x9d often refers to actions taken prior to precipitation in order to prevent ice buildup, in contrast to the term xe2x80x9cde-icingxe2x80x9d which often refers to actions taken after precipitation to remove ice buildup. However, these terms are often also used interchangeably with one another. These conventional anti-icing and de-icing actions take the forms of chemical, thermal, and mechanical methods, as will now be summarized.
Anti-icing chemicals prevent ice buildup by lowering the melting temperature of water to a temperature below that of the ambient temperature, thus preventing the formation of ice. These chemicals are also used to melt ice, in the de-icing context, although with poorer efficiency than if used prior to formation of the ice. Examples of anti-icing and de-icing chemicals include the salts of sodium chloride, calcium chloride, and magnesium chloride. Of these three salts, sodium chloride is the least expensive, but is only effective to a temperature of about xe2x88x9212xc2x0 to xe2x88x9218xc2x0 C. Sodium chloride also involves significant environmental impact, because of its tendency to increase groundwater salinity, its undesirable effects on fragile aquatic ecosystems, and its effect of leaching soil toxins into groundwater and surface water; sodium chloride also tends to crack the top surface of concrete roadways. Calcium chloride reduces the melting temperature of water to xe2x88x9229xc2x0 C. and is less damaging to concrete, but can be more damaging to the environment. Calcium chloride and sodium chloride are also quite corrosive to the vehicles themselves, and corrosive to the steel that is often used to reinforce concrete bridge decks. Magnesium chloride is know to reduce the melting point of water to xe2x88x9233xc2x0 C. and is believed to be less environmentally damaging and less corrosive, but is significantly more expensive than the other salts. In addition, the dispensing of anti-icing chemicals often involves significant labor costs.
Thermal anti-icing techniques involve the heating of the roadway surface to keep its temperature above the melting point of water. For example, U.S. Pat. No. 3,995,965 discloses a heating system including ducts at the surface of the roadway for carrying heating fluid, in which the fluid is pumped in response to a vehicle passing over an actuator. In recent years, test projects have been built in Oregon and in Virginia to evaluate the heating of bridge decks. One of the Oregon projects reportedly involves the heating of a bridge deck that is over 1000 meters in length, using a mineral insulate cable. Another bridge project in Oregon evaluated the use of heated ground water that is pumped through thermoplastic tubing in the bridge deck. The Virginia Department of Transportation projects heats a bridge deck with ammonia carried by steel piping in the bridge deck; the ammonia is heated via a heat exchanger, in which the primary loop carriers a mixture of propylene glycol and water that is heated by a gas-fired furnace. In this Virginia system, a computerized control system activates the bridge heating upon detecting of snow or ice, or upon detecting freezing temperatures in combination with precipitation or a wet bridge deck; the control system also shuts down the heating cycle upon detecting safe conditions.
These conventional thermal anti-icing methods necessarily involve significant construction costs to place the cable or pipe, and are generally not very energy efficient considering that the entire bridge deck is being heated. In addition, if the hazardous conditions (i.e., wet and freezing) continue, the bridge deck continues to be heated, consuming additional energy.
Mechanical methods are generally used for de-icing, rather than anti-icing. Examples of these methods include simply the plowing and bulldozing of ice and snow on the roadways by plowing vehicles.
By way of further background, the application of anti-skid elements to road surfaces is know. A fundamental example of this approach is simply the dispensing of sand over ice and snow, to provide additional friction between the frozen surface and the tires of passing vehicles. Of course, sand and other abrasives do not themselves serve to melt ice and snow, and as such abrasives are often used in combination with chemical de-icing chemicals. Examples of such anti-skid elements, in the form of road or walkway markers or marking tape, are disclosed in U.S. Pat. No. 4,146,635, U.S. Pat. No. 5,316,406, German Patent No. DE 2702442, and U.S. Pat. No. 5,204,159. A description of heat insulation materials for frozen roads is disclosed in Soviet Union Patent No. 1010889-A1.
In recent years, significant research in the field of highway safety improvement has been funded by the United States Department of Transportation. This research includes the use of thin bonded overlays or surface laminates of highway pavements and bridge decks. Several test projects of various bonded overlays and inlays of highway surfaces, and of non-corrosive lightweight thin overlays for bridges, have been carried out. Computer modeling programs for the estimation of pavement and bridge resurfacing life and costs, as well as pavement simulation machines, have also been developed.
By way of still further background, super insulator materials are known. These materials would improve the energy efficiency of thermal anti-icing methods. For example, silica aerogel has the known properties of extremely light weight, and excellent thermal insulating properties. Another known thermal insulator with excellent properties is the THERMAL DIODE coating developed by 27th Century Technologies, Inc. This coating is described as creating an effectively one-way super-conducting path for thermal energy in one direction, but an excellent thermal insulator in the opposite direction. By way of still further background, one type of known tire stud material remains flexible and pliable under warm temperatures, but changes its molecular structure under freezing temperatures to become rigid.
By way of still further background, remote and on-site actuation of the dispensing of liquid chemical anti-icing agents onto the driving surfaces of bridges, tunnels, ramps, and roadways, is also known in the art.
It is therefore an object of the present invention to provide a system for preventing the buildup of ice on a roadway or bridge deck by preventing the bonding of ice to the road surface.
It is a further object of this invention to provide such a system having a road cover that can be readily removed and replaced, for example with the change of season.
It is a further object of this invention to provide such a system that utilizes mechanical anti-icing, based on force applied by the vehicles themselves, to prevent ice buildup.
It is a further object of this invention to provide such a system that efficiently utilizes chemical anti-icing agents to minimize chemical runoff, and without requiring human intervention and labor.
It is a further object of this invention to provide such a system in which thermal anti-icing techniques are applied to the road surface in an extremely efficient manner.
It is yet a further object of this invention to provide such a system in which mechanical, thermal, and chemical anti-icing techniques are synergistically combined to maximize chemical and energy efficiency of the anti-icing process.
It is a further object of this invention to provide such a system that increases road surface traction on icy roads at freezing temperatures, but which provides a relatively smooth road surface at warmer temperatures.
Other objects and advantages of the present invention will be apparent to those of ordinary skill in the art having reference to the following specification together with its drawings.
The present invention may be implemented by way of a deformable road cover that is applied along the length of the roadway in strips that substantially match the width of vehicle tire paths. The road cover includes a layer having numerous parallel tubes that are adjacent to one another, and that are oriented transversely to the direction of travel. The tubes are deformable when driven across, with the exception of periodically selected ones of the tubes that are instead expanded or otherwise made incompressible; these non-deformable tubes provide increased friction for the tires of the overpassing vehicles. The road cover is preferably held in place on the roadway magnetically, and may be removed and replaced by way of rollers carried on a truck.
According to another aspect of the invention, thermal anti-icing can be combined into the road cover by including electric heating wire elements into selected ones of the parallel tubes; a highly thermally insulating layer is preferably disposed under the road cover, so that heat is directed only to the road cover surface and not to the underlying roadbed. The thermal efficiency provided by this road cover is therefore maximized.
According to another aspect of the invention, anti-icing chemicals are pumped through selected ones of the tubes, with these tubes having small orifices at their surface so that the chemicals are dispensed to the surface of the road cover. A reservoir of the chemical anti-icing chemical is maintained in an overhead reservoir, so that the chemicals are gravity fed to the road surface through a temperature-controlled valve. The deforming action of the parallel tubes under the weight of passing vehicles assists to dispense the anti-icing chemicals, and the tires of the passing vehicles distributes the dispensed chemicals.
According to another aspect of the invention, mechanical, thermal, and chemical anti-icing techniques are synergistically combined into a single road cover system. This combination provides excellent anti-icing performance while maximizing energy and chemical usage efficiencies, and minimizing run-off pollution.